Toxicity Assessment of 6-Deoxytetrodotoxin by Mouse Bioassay and Its Distribution in Pufferfish

Tetrodotoxin (TTX, 1) is a potent neurotoxin that occurs in a wide range of marine and terrestrial organisms. 6-DeoxyTTX (2) was isolated from pufferfish as a low-abundance TTX analogue. Although the toxicities of major TTX analogues have been investigated, the acute toxicity and biological distribution of 6-deoxyTTX remain poorly understood because of limited availability of purified or synthetic 6-deoxyTTX. In this study, acute toxicity of 6-deoxyTTX was evaluated based on mouse bioassay. The toxicity of 6-deoxyTTX was estimated to be 1 MU = 570 ng, with an LD99 value of 28 μg/kg. Based on comparison with the LD99 value of TTX (10 μg/kg), the relative potency of 6-deoxyTTX was estimated to be 0.36, indicating higher toxicity than other deoxy analogues. In addition, high-resolution LC–MS analysis revealed the occurrence of 6-deoxyTTX in toxic pufferfish species in the genera Takifugu, Arothron, and Lagocephalus. Although 6-deoxyTTX was generally present at much lower concentrations than TTX, 6-deoxyTTX should be considered a toxicologically relevant analogue because of its relatively high acute toxicity. These results demonstrate that 6-deoxyTTX is a low-abundance TTX analogue with relatively high toxicity, providing new information relevant to food safety assessment and the distribution of TTX analogues in pufferfish.